1. Field of the Invention
This invention relates to a vehicle muffler system and more particularly pertains to a muffler system that is mounted within an engine housing and includes a venturi extracting heat shield surrounding the muffler which uses the exhaust gases expelled from the muffler for creating an air flow that draws heat from the engine housing and from around the surface of the muffler for discharge externally of the housing.
2. Description of the Prior Art
During the last few years, noise pollution has become a sufficiently serious problem to cause cities and other governmental agencies to set maximum permissible noise standards for garden tractors or the like. In order to comply with these minimum noise standards, mufflers of certain of these garden tractors have been placed within the engine housing of such tractors in order to use the housing itself as an additional sound barrier. However, the hot exhaust gases passing through the muffler creates a considerable amount of heat in the engine housing. Although some of this heat is removed from the housing by means of air circulated by the engine cooling fan, it has been found desirable to remove more heat from the engine housing for operator comfort and in order to reduce maintenance problems and provide for more efficient operation of the vehicle. The U.S. Pat. No. to Nemschoff, 3,884,322, which is assigned to the assignee of the present invention, discloses such a prior art garden tractor with a muffler within its engine housing.
The use of power driven fans within engine housings is, of course, a well known means of removing heat from the engine housing of a vehicle housing. Also, movement of the vehicle at a sufficient speed through the air is another well known way of removing heat from engine compartments of a vehicle.
The desirability of extracting heat from an engine housing having a muffler therein is also taught by U.S. Pat. No. 3,795,287 which issued to Rose on Mar. 5, 1974. Rose discloses a snowmobile muffler which has a radial inlet pipe and a radial outlet pipe. A concentric two-piece shield is provided to guide air between the muffler and the shield to cool the muffler and also to reduce the ambient temperature of the engine compartment. The shield inlet opening and outlet opening are axially elongated slots in the shield. Thus, this patented structure performs the same function as the subject device but in a different way since the patentee does not rely on the venturi effect to draw air past the muffler but relies on the forward speed of the vehicle (or a cooling fan) to create the cooling flow of air.
Desmond U.S. Pat. No. 1,025,251 recognizes that exhaust gases can be used to create an air flow past the cylinder walls of an air cooled engine that is apparently not confined in a housing. Desmond discloses a double walled cylinder having air passages therebetween through which air passes before being drawn into a muffler housing. The exhaust gases are directed through a pipe that terminates in a constricted area or venturi to increase the velocity of the exhaust gases at that point. The high velocity exhaust gas induces active circulation of air between the two walls of the cylinder for the purpose of cooling the cylinder walls. This patent differs from the present invention in that the patentee's muffler itself defines the heat shield and is sealed to the exhaust pipe at one end, whereas the heat shield of the subject invention is spaced from the muffler, is open at both ends, and also draws heated air from an engine housing.
U.S. Pat. No. 2,363,236 which issued to Flour on Nov. 21, 1944 discloses an air cooled muffler with the exhaust gases passing through a venturi into a throat for inducing a high velocity flow of air along the exhaust pipe and muffler. The muffler receives exhaust gases from an engine through an exhaust pipe. The muffler is enclosed within an outer conduit or stack that includes a cylindrical shell section, a cone, and a nipple 33. Although Flour discloses the concept of cooling a muffler that is outside of the engine housing by using exhaust gases to induce an air flow therepast, he does not suggest anything about extracting heated air from the engine housing.